Abstract
BackgroundThe switch from photosynthetic or predatory to parasitic life strategies by apicomplexans is accompanied with a reductive evolution of genomes and losses of metabolic capabilities. Cryptosporidium is an extreme example of reductive evolution among apicomplexans, with losses of both the mitosome genome and many metabolic pathways. Previous observations on reductive evolution were largely based on comparative studies of various groups of apicomplexans. In this study, we sequenced two divergent Cryptosporidium species and conducted a comparative genomic analysis to infer the reductive evolution of metabolic pathways and differential evolution of invasion-related proteins within the Cryptosporidium lineage.ResultsIn energy metabolism, Cryptosporidium species differ from each other mostly in mitosome metabolic pathways. Compared with C. parvum and C. hominis, C. andersoni possesses more aerobic metabolism and a conventional electron transport chain, whereas C. ubiquitum has further reductions in ubiquinone and polyisprenoid biosynthesis and has lost both the conventional and alternative electron transport systems. For invasion-associated proteins, similar to C. hominis, a reduction in the number of genes encoding secreted MEDLE and insulinase-like proteins in the subtelomeric regions of chromosomes 5 and 6 was also observed in C. ubiquitum and C. andersoni, whereas mucin-type glycoproteins are highly divergent between the gastric C. andersoni and intestinal Cryptosporidium species.ConclusionsResults of the study suggest that rapidly evolving mitosome metabolism and secreted invasion-related proteins could be involved in tissue tropism and host specificity in Cryptosporidium spp. The finding of progressive reduction in mitosome metabolism among Cryptosporidium species improves our knowledge of organelle evolution within apicomplexans.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3343-5) contains supplementary material, which is available to authorized users.
Highlights
The switch from photosynthetic or predatory to parasitic life strategies by apicomplexans is accompanied with a reductive evolution of genomes and losses of metabolic capabilities
We sequenced the genomes of six C. ubiquitum and C. andersoni isolates and conducted a comparative genomic analysis of Cryptosporidium spp. and other well-studied apicomplexans
We focused on reductive evolution in energy metabolism and differential evolution of invasion-related proteins among Cryptosporidium species, as they may be involved in tissue tropism and host specificity
Summary
The switch from photosynthetic or predatory to parasitic life strategies by apicomplexans is accompanied with a reductive evolution of genomes and losses of metabolic capabilities. About 30 Cryptosporidium species have been recognized in humans, livestock, companion animals, and wild vertebrates [10] They differ from each other in host specificity and predilection sites [10]. C. hominis is largely a pathogen of humans and nonhuman primates, C. parvum is a major pathogen in ruminants. Another intestinal Cryptosporidium species, C. ubiquitum, has been detected in humans in industrialized nations [12, 13]. Like C. hominis, most other recognized Cryptosporidium species have some host specificity [10]
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